1. Field
The technology described herein relates to temperature calibration and temperature compensation of oscillators having mechanical resonators.
2. Related Art
Oscillators are ubiquitous components in electronic equipment including wireless and wireline communications systems, entertainment electronics, aerospace systems, and timing systems. The oscillators traditionally are used to provide a reference signal or clock signal, such that precision of the signal frequency is important. Conventionally, crystal oscillators having quartz crystals as the resonating element have served as the oscillators of choice because they can be manufactured to provide precise signal frequencies within ±1.5 parts-per-million (ppm) of a target frequency value, frequency stabilities of ±2.5 ppm over the entire operating temperature range from −40° C. to +85° C., tunability of up to ±15 ppm, aging of below ±1 ppm/year (at 25° C.), typical phase noise of −138 dBc/Hz at 1 kHz, and power consumption as low as 1.5 mA.
Different categories of crystal oscillators have developed, including crystal oscillators (XO), temperature compensated crystal oscillators (TCXO), and oven-controlled crystal oscillators (OCXO). The TCXO is very similar to the XO, except that the compensation uses a temperature sensor and a tuning circuit that allows the frequency of the quartz crystal resonator to be corrected depending on the temperature. As a result the temperature stability of a typical XO of about ±10 ppm can be reduced down to ±1.5 ppm or even ±0.5 ppm.